1. Field of the Invention
The invention relates to a method of producing an antifriction element, in particular a friction bearing half-shell, by means of which at least one coating is applied to at least one surface of the antifriction element, in particular to a surface with a concave curvature, and the antitriction element is displaced through a particle flow at least partially forming the coating.
2. Description of the Prior Art
Methods of applying metallic layers to a metallic base under vacuum have long been known. DE 195 14 835 C1 corresponding to U.S. Pat. No. 5,955,202, for example, discloses a method of applying a coating to concave antifriction elements by vapour-deposition. To this end, a specific distance is set between the base and the surface of the vapour bath. The substance to be deposited is disposed in evaporator pans and evaporation is operated by means of electron radiation. The substrate is guided through the particle flow as it forms so that, as the coating is being vapour-deposited, the evaporator and the base body are displaced at a non-uniform speed relative to one another. The speed of the linear motion reaches its maximum component both as it enters and leaves this beam of vapour. In order to ensure in addition that the thickness of the vapour-deposited coating does not vary by more than 15% from the minimum thickness of the layer, parts of the vapour flow are masked by screens.
The disadvantage of this type of vapour deposition is that the layer thickness is determined by various parameters which have to be reconciled with one another and a relatively complex sequence of motions needs to be programmed and monitored or controlled. In addition, structural components have to be used in order to achieve the desired ratio of coating thicknesses.
The underlying object of the present invention is to provide a method of the type outlined above which requires no structural components placed in the particle flow needed to produce coatings with a specific coating thickness profile.
This object is achieved by guiding the antifriction elements through the particle flow in rotating motion about an axis perpendicular to a longitudinal median axis of the particle flow or parallel with a length of a device containing the substance to be deposited. The antifaction element is rotated by less than 180xc2x0 between entering and leaving the particle flow, and one side and the crown of the concave surface of the antifriction element is at least partially masked or screened by the antifriction element itself due to the rotating motion and, secondly, every region of the curved surface of the antifriction element assumes at least more or less the same position relative to the particle flow during the rotation, so that the quantity precipitated onto the sides of the substrate match the quantity in the crown region of the antifriction element, thereby enabling a largely uniform coating thickness to be produced. Accordingly, no additional screens need to be provided at the centre of the particle flow. Another advantage as compared with the known method is that this method enables large-sized bearings to be coated, such as used in motors outside the automotive industry, i.e. with a radius of more than 150 mm.
Yet another advantage is obtained if the rotating motion is combined with a linear motion having a velocity component perpendicular to the longitudinal median axis of the particle flow and/or the velocity component of the linear motion perpendicular to the rotating motion, since the linear motion provides one possible way of coating individual components and their direction of displacement can be adjusted to best suit the coating conditions.
Another advantage is the fact that the linear motion is effected continuously and/or in the same pattern, which reduces the technical complexity of this method accordingly, as compared with the method known from the prior art.
Another advantage is the fact that end faces of the antifriction element are aligned at least approximately parallel with the particle flow longitudinal median axis or particle flow, in particular with a line externally bounding the propagation of the particle flow, since this helps to keep the coating thickness of the deposited coating uniform.
Rotation of the antifriction element by less than 180xc2x0 between entering the particle flow and leaving the particle flow will produce complete coverage of the concave surface generally used with antifriction elements of this type and enable the rotation of the antifriction elements to be adjusted to suit the specific antifriction element.
Another embodiment also offers advantages, whereby the particle flow is limited by laterally disposed aperture screens between the antifriction element and the device containing the substance to be vapour-deposited and a rotation angle of the rotary motion is adapted to the aperture cross section of the aperture screens and resultant particle flow so that the timing of the rotary motion can be optimised, thereby reducing cycle times and making the process more economical.
A different embodiment is possible, in which the antifriction element is aligned on a rotary element, e.g. a rotating drum, a turntable or similar, whose rotation axis is directed perpendicular to the particle flow longitudinal median axis, the advantage of this being that several antifriction elements can be economically coated during one process step.
Another advantage of this arrangement is that several antifriction elements are disposed individually in separate compartments on the rotary element, thereby preventing individual antifriction elements from being damaged by others.
In another advantageous variant of the method, the compartments are designed so that at least one antifriction element can be inserted or at least one antifriction element removed via a gating system during radiation, thereby enabling a continuous production process to be operated.
In another embodiment, the diameter of the rotary element is adapted to the diameter and/or radius of the antifriction elements with the advantage that antifriction elements of different sizes can be coated.
Also of advantage is another embodiment in which the speed of the rotary motion is set depending on a coating thickness, thereby enabling different coating thicknesses to be produced.
Another advantage is the fact that the speed of the rotary motion can be varied, preferably continuously, during rotation thereby enabling distribution of the coating thickness to be selectively varied within a large range across the surface to be coated.
Another advantage is the fact that a multiple coating can be applied by rotating the rotary element several times, which offers a simple way of producing multiple coatings and/or forming an alloy for the coating to be applied or applying the coating in several steps.